1. Technical Field
This invention relates generally to an apparatus for forming plastic-coated paperboard containers, and is particularly concerned with an apparatus for forming and sealing a denesting flap extension into a denesting lip or skirt on nestable or stackable, plastic-coated paperboard containers. The purpose of the denesting lip is to facilitate the removal of each individual container taken from a nested stack of such containers. More particularly, this invention relates to an automatic apparatus for breaking or folding a flat container blank, forming it into a container, and sealing the bottom of the paperboard container while also breaking, forming and sealing the denesting lip on one side at the top end of the container.
2. Background Art
In the packaging of fluids such as milk, juices, soups and soft drinks as well as certain powders and other items, extensive use has been made of containers formed of paperboard sheet material having an overall coating of thermoplastic film, such as polyethylene applied on both surfaces of the sheet. This plastic coated paperboard is impervious to moisture and is particularly suitable for use in the packaging of such liquids. The thermoplastic coating not only serves to moisture proof the walls of container, but also can be utilized for sealing the seams of the container. This sealing action can be accomplished by heating the surfaces to be sealed ultrasonically or otherwise, and then pressing the surfaces tightly together to form a liquid tight, plastic-to-plastic bond. Machines for forming, filling and sealing such containers are known in the art. One method and device for sealing the bottom of such containers is illustrated in U.S. Pat. No. 4,601,425 issued to Bachner and entitled "Nonwicking Bottom Closure for a Liquid-tight Container."
The focus of the present invention is an apparatus for forming and sealing a denesting lip in paperboard containers having a generally truncated, tapered form. The present invention is adapted to be used with prior art machines that form, fill and seal paperboard containers. A container having such a denesting lip or skirt is illustrated in U.S. Pat. No. 4,498,585 to Gordon et al. This type of container, with a denesting lip, is particularly appropriate for fast food restaurants, delicatessens or other food and beverage outlets wherein containers need to be taken one at a time from a nested stack readily without their locking or sticking together. It also will be recognized that use of this invention is not limited to tapered containers having trapesoidal sides, but may be used for any container configuration (i.e., tapered or untapered, and having a round, curved or polygonal cross-section) having one end open so that a plurality of such cartons may be stacked or nested, one partially inside the other.
One object of the present invention is to provide an automatic apparatus for forming and sealing, from a denesting flap extension on a carton blank, a denesting lip or skirt on containers of the type illustrated in U.S. Pat. No. 4,498,585. Another object of the present invention is to form the denesting lip at the same time that another portion of this apparatus is forming the paperboard container into its three dimensional shape and sealing the bottom of the paperboard container. Another object of this invention is to form a smooth, flat surface on the bottom of the container. Another object of the present invention is to use the same sealing means, whether ultrasonic, radient heat or hot or cold adhesives, to seal both the denesting lip and the bottom opening of the paperboard container. A further object of the present invention is to provide spring-loaded pressure pads to prevent the paperboard container from slipping down while the denesting lip is being formed, thus ensuring denesting lips of uniform size and configuration.